1. Field of the Invention
This invention relates in general to orthodontics and more particularly to methods and kits for for providing pontics in orthodontic appliances.
2. Description of the Background Art
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as “braces.” Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time-consuming process requiring many visits to the orthodontist's office. Moreover, from a patient's perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such an appliance may be comprised of a thin shell of elastic material, referred to as an “aligner” that generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth configuration. Placement of an aligner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate arrangements to a final desired arrangement. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
Systems of preformed aligners employing technology described in U.S. Pat. No. 5,975,893, are commercially available from Align Technology, Inc., Santa Clara, Calif., under the tradename Invisalign® System. Align Technology, Inc., is the assignee of the present application. The Invisalign® System relies on designing and fabricating the aligners to be worn by the patient throughout treatment. The design of the aligners relies on computer modeling of a series of successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and to reposition the teeth to each of said tooth arrangements. Usually, the set of aligners which is designed and fabricated at the outset of the treatment is able to successfully reposition the teeth to a final desired arrangement.
With the Invisalign® System, as well as with other conventional orthodontic treatment systems, it is sometimes necessary to extract one or more teeth prior to tooth repositioning. At present, the Invisalign® System does not provide for filling in the space or void which remains within the aligner after the tooth is extracted with a structural component such as an artificial tooth which is commonly referred to as a dental pontic.
The design and fabrication of dental pontics are described in U.S. Pat. Nos. 6,186,790; 6,050,820; 6,049,743 and 5,613,845, the full disclosures of which are incorporated herein by reference. Currently, dental professionals trained in the use of the Invisalign orthodontic system are using a variety of materials and techniques known in the art to fabricate dental pontics which can be worn in the aligner extraction site(s). The most commonly employed materials are tooth-shaded dental composites typically used to repair carious lesions or fabricate provisional (temporary) crowns and bridges. These materials consist mainly of a polymer matrix and dispersed reinforcing inorganic filler particles. Typical polymers used are based on dimethacrylate such as Bis-GMA or urethane dimethacrylate (UDMA). Quartz, lithium aluminum silicate and barium, strontium, or zinc glasses have been commercially distributed as fillers. Typically these materials are packaged as a two-paste (base/catalyst) system. The polymer matrix may be visible light curable, self-curing, dual curing, and vacuum, heat and pressure curable compositions as well as any combination thereof. A popular method for mixing and dispensing these materials involves the use of an automix system whereby a dispensing gun is utilized to dispense the base and catalyst, which are in separate cartridges, through a mixing cannula directly into the extraction site. Commercial examples of the autopolymerizing composites are Luxatemp Plus (DMG/Zenith), Integrity (Dentsply/Caulk), Protemp Garant (ESPE) and Turbo Temp (Danville Engineering). Alternatively light cured composites may be used to fabricate dental pontics. Commercial examples of light cured composites are Revolution (Kerr), Star-Flow (Danville Engineering), and Tetric (Vivadent). Other useful dental composite materials are based on the methyl methacrylate polymer. Such acrylic polymers are well known and commercially available for example as Jet Tooth Shade self-curing acrylic resin by Lang Dental.
Although dental composites have been used to fabricate dental pontics for the Invisalign system there remain two important disadvantages to using these materials. First the ability of these materials to bond to the aligner thermoplastic is poor and second these materials are very stiff and non-flexing. These characteristics significantly compromise retention of the pontic in the aligner especially if it is subjected to torsional or flexing forces such as when the aligner is either being inserted or removed from a patient's mouth or while the patient is cleaning their aligner using a cleaning device such a toothbrush or denture brush.
While it has been proposed to paint or color a portion of the aligner which overlies the void (see co-pending application Ser. No. 09/454,278, the full disclosure of which is incorporated herein by reference), partial coloring of the aligner can affect the light transmitting properties and be unaesthetic and the lack of any underlying structure can weaken or lessen the resilience of the aligner and limit its effectiveness.
For these reasons, it would be desirable to provide methods, systems, and kits for modifying an aligner to accommodate patients who have had teeth extracted prior to treatment with an aligner or other polymeric shell orthodontic appliance. It would be particularly desirable if the methods would permit an orthodontist or other clinician to modify an aligner or other orthodontic appliance in the professional office, rather than having the modification done at the time of fabrication or at an off-site location. It would be further desirable still if the aligner could be modified by the treating clinician, fitted with the patient, and further modified if necessary for patient comfort or other reasons. The resulting modified aligners or other orthodontic appliances should be esthetically pleasing, and preferably should mask the absence of an underlying tooth while the aligner or other appliance is worn. At least some of these objectives will be achieved by the inventions described hereinafter.
U.S. Pat. No. 5,975,893, and published PCT application WO98/58596, have been described above. Co-pending application Ser. No. 09/454,278, which has been published as WO99/028,228, relates to the fabrication of aligners which have been colored to cover a void left where teeth have been removed. The full disclosures of each of these patents and pending applications are incorporated herein by reference.